U.S. Pat. No. 1,075,350 describes an apparatus for mixing and depositing concrete. A supply train consists of a plurality of wagons containing sand, aggregate and cement. At both sides of the train belt conveyors are arranged end to end in overlapping relation. The mixing materials, i.e. aggregate, cement etc. fall by gravity through side outlets onto the conveyors and are conveyed theron into side hoppers of a leading wagon. From here the materials are elevated by side elevators and fall in bunkers from which they are metered by rotary measures into a mixer. Water is added and a continuous stream of concrete is produced and leaves the apparatus along an inclined belt conveyor at the front of the train. This apparatus indeed can be used to concrete overground surfaces, however, because of the side conveyors and the elevators its dimensions, i.e. width and height are too great to use it in tunnels. Further, the plurality of measuring devices are expensive if high precision is required.
The periodical "Tunnels and Tunnelling, March, 1986" describes a method for the production of concrete within a tunnel. A rail mounted concreting train comprises a wagon provided with three silos one behind another. The first silo contains two equal weighed batches of cement and the other two silos contain one weighed batch of aggregate respectively. The three silos are weigh-batched outside the tunnel. After both batches have been separately used, the wagon must be taken out of the tunnel for reloading and replaced by the next full one. Cement and aggregate at the same time fall on a belt conveyor below the silos and are conveyed forwards and via a further steep conveyor into a mixer where a defined quantity of water is added. A main disadvantage of this proposal resides in that the batches must be weighed outside the tunnel. The two batches result in 4 m.sup.3 concrete. Thereafter the supply wagon must be returned to the supply station outside the tunnel before the next full one can be run in. In the case of long tunnels the lost time is too great. Further the proportion of the mixing components cannot be adapted onto the momentary requirements. The large batches require a corresponding large mixer. Large volume mixers again require longer mixing periods. The common transport of cement and aggregate on the bottom conveyor and steep conveyor results in a remarkable cement loss, because the down-falling cement cannot be completely collected on the bottom conveyor belt. Also a cement dust generation cannot be avoided.